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Posted to commits@cassandra.apache.org by "Jon Haddad (Jira)" <ji...@apache.org> on 2025/03/07 20:50:00 UTC
[jira] [Comment Edited] (CASSANDRA-19564) MemtablePostFlush deadlock leads to stuck nodes and crashes
[ https://issues.apache.org/jira/browse/CASSANDRA-19564?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17840986#comment-17840986 ]
Jon Haddad edited comment on CASSANDRA-19564 at 3/7/25 8:49 PM:
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I'm closing this out as I'm no longer seeing the issue after moving from ZFS to XFS, with some reservations. I'm a little concerned that I haven't noticed compaction affected by this unlink issue, only the commit log unlinking during the PostFlush. It's possible this also affected unlinking during compaction and we just didn't notice it, because the blocking PostFlush causes cascading failure whereas blocking compaction from unlinking would only cause compaction to take longer. I am not sure how long the filesystem call was waiting, only that it was at least 10 seconds.
was (Author: rustyrazorblade):
I'm closing this out as I'm no longer seeing the issue, with some reservations. I'm a little concerned that I haven't noticed compaction affected by this unlink issue, only the commit log unlinking during the PostFlush. It's possible this also affected unlinking during compaction and we just didn't notice it, because the blocking PostFlush causes cascading failure whereas blocking compaction from unlinking would only cause compaction to take longer. I am not sure how long the filesystem call was waiting, only that it was at least 10 seconds.
> MemtablePostFlush deadlock leads to stuck nodes and crashes
> -----------------------------------------------------------
>
> Key: CASSANDRA-19564
> URL: https://issues.apache.org/jira/browse/CASSANDRA-19564
> Project: Apache Cassandra
> Issue Type: Bug
> Components: Local/Compaction, Local/Memtable
> Reporter: Jon Haddad
> Assignee: Runtian Liu
> Priority: Urgent
> Fix For: 4.1.x
>
> Attachments: image-2024-04-16-11-55-54-750.png, image-2024-04-16-12-29-15-386.png, image-2024-04-16-13-43-11-064.png, image-2024-04-16-13-53-24-455.png, image-2024-04-17-18-46-29-474.png, image-2024-04-17-19-13-06-769.png, image-2024-04-17-19-14-34-344.png, screenshot-1.png
>
>
> I've run into an issue on a 4.1.4 cluster where an entire node has locked up due to what I believe is a deadlock in memtable flushing. Here's what I know so far. I've stitched together what happened based on conversations, logs, and some flame graphs.
> *Log reports memtable flushing*
> The last successful flush happens at 12:19.
> {noformat}
> INFO [NativePoolCleaner] 2024-04-16 12:19:53,634 AbstractAllocatorMemtable.java:286 - Flushing largest CFS(Keyspace='ks', ColumnFamily='version') to free up room. Used total: 0.24/0.33, live: 0.16/0.20, flushing: 0.09/0.13, this: 0.13/0.15
> INFO [NativePoolCleaner] 2024-04-16 12:19:53,634 ColumnFamilyStore.java:1012 - Enqueuing flush of ks.version, Reason: MEMTABLE_LIMIT, Usage: 660.521MiB (13%) on-heap, 790.606MiB (15%) off-heap
> {noformat}
> *MemtablePostFlush appears to be blocked*
> At this point, MemtablePostFlush completed tasks stops incrementing, active stays at 1 and pending starts to rise.
> {noformat}
> MemtablePostFlush 1 1 3446 0 0
> {noformat}
>
> The flame graph reveals that PostFlush.call is stuck. I don't have the line number, but I know we're stuck in {{org.apache.cassandra.db.ColumnFamilyStore.PostFlush#call}} given the visual below:
> *!image-2024-04-16-13-43-11-064.png!*
> *Memtable flushing is now blocked.*
> All MemtableFlushWriter threads are Parked waiting on {{{}OpOrder.Barrier.await{}}}. A wall clock profile of 30s reveals all time is spent here. Presumably we're waiting on the single threaded Post Flush.
> !image-2024-04-16-12-29-15-386.png!
> *Memtable allocations start to block*
> Eventually it looks like the NativeAllocator stops successfully allocating memory. I assume it's waiting on memory to be freed, but since memtable flushes are blocked, we wait indefinitely.
> Looking at a wall clock flame graph, all writer threads have reached the allocation failure path of {{MemtableAllocator.allocate()}}. I believe we're waiting on {{signal.awaitThrowUncheckedOnInterrupt()}}
> {noformat}
> MutationStage 48 828425 980253369 0 0{noformat}
> !image-2024-04-16-11-55-54-750.png!
>
> *Compaction Stops*
> Since we write to the compaction history table, and that requires memtables, compactions are now blocked as well.
>
> !image-2024-04-16-13-53-24-455.png!
>
> The node is now doing basically nothing and must be restarted.
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